The present invention relates to a color agent for a road marking material and a road marking material using the color agent. More particularly, to a color agent for a road marking material, which contains no harmful elements and exhibits excellent tinting strength, hiding power, light resistance and heat resistance, and which is suppressed in surface activity thereof, and a road marking material using the color agent, which shows a less change in hue with the passage of time and an excellent retroreflective property.
Hitherto, white or yellow road marking materials have been used to form zone lines, road signs, etc., for the purpose of obeying traffic laws and regulations and preventing or minimizing traffic accidents.
On the other hand, in recent years, various characters or complicated marks have been frequently used in Japan as road markings. Thus, green- or brick-colored road marking materials have been applied to school zones, bicycle roads, etc. Further, in Japan it has been demanded to use designed color marks in community squares, shopping roads, jogging courses, cycling roads, promenades, parks, etc., in order to expect environmental beautification or PR effects.
The road marking materials are classified into cold-applied paint-types (first class), heat-applied paint-types (second class) and melt types (third class) according to JIS K 5665. Further, corresponding to the above color marks, there are known adhesion-type road marking materials such as heat-adhesion types and cold-adhesion types.
Any of the above road marking materials is used outdoors for a long period of time and, therefore, is required to have a less change in hue with the passage of time after application to roads. It is known that the change in hue of the road marking materials is caused by discoloration of color agents or deterioration of resins due to ultraviolet radiation or acid rain, deterioration of resins due to high surface activity of color agents, or the like. Thus, the color agents used in the road marking materials are required to exhibit a high weather resistance as well as a low surface activity.
Also, among the above-mentioned road marking materials, the melt-type road marking materials (third class) are heated and molten at a temperature as high as about 200° C. For this reason, color agents used in such melt-type road marking materials are required to show a heat resistance capable of preventing discoloration thereof even when heated at such a high temperature.
In addition, in order to shield a road surface made of asphalt or concrete and allow a road surface to show the aimed hue, the color agents used in the above road marking materials are also required to have excellent hiding power and tinting strength.
Among the road marking materials, the yellow road marking materials for traffic signs are especially important to users, since the yellow color is intended to indicate regulations or cautions on traffic. The hue of the yellow color used for these purposes is unified as a common “yellow for traffic signs or markings” by the National Police Agency in Japan.
The yellow road marking materials tend to be deteriorated in reflectivity as compared to white road marking materials. In particular, it is known that when only a small amount of light emitted from headlight or street lamps such as mercury lamp and sodium lamp is present during the night, the visibility of the yellow markings is considerably low as compared to that during the daytime. Therefore, the color agents used in the yellow road marking materials are required to be free from discoloration even when exposed to a long-term outdoor use and when melted under a high temperature condition, to show a hue lying within the common “yellow for traffic signs or markings”, and to have an excellent night reflectivity.
At present, lead chromate has been mainly used as pigments for the yellow road marking materials because of not only excellent heat resistance and weather resistance but also clear hue thereof. However, the lead chromate contains heavy metals such as chromium and lead. For this reason, it has been demanded to provide alternate yellow pigments from the standpoints of hygiene, safety and prevention of environmental pollution.
As yellow pigments for road marking materials other than lead chromate, there are known inorganic pigments such as titanium yellow, iron oxide hydroxide and bismuth vanadate; and yellow-based organic pigments such as azo-based, isoindolinone-based and anthraquinone-based pigments.
However, although the above inorganic pigments are excellent in heat resistance and weather resistance, these pigments tend to be deteriorated in tinting strength, thereby failing to show a clear hue. On the other hand, the above organic pigments usually show a clear hue, but tend to be deteriorated in hiding power as well as heat resistance and light resistance. Thus, any of the conventional inorganic and organic pigments fails to satisfy properties required as alternate materials of lead chromate. Further, it is known that road marking materials using such color agents tend to be deteriorated in visibility during the night.
Hitherto, in order to obtain pigments as alternate materials of lead chromate which are free from environmental pollution, and improved in weather resistance and heat resistance as well as visibility during the night, it has been attempted to combine the inorganic pigments with the organic pigments (Japanese Patent Application Laid-Open (KOKAI) Nos. 4-132770(1992), 7-331113(1995), 8-209030(1996), 9-100420(1997) and 2001-220550, etc.).
At present, it has been strongly required to provide a color agent for a road marking material which shows a less change in hue with the passage of time and is capable of producing such a road marking material exhibiting an excellent retroreflective property. However, such color agent has not been obtained until now.
That is, in the methods described in Japanese Patent Application Laid-Open (KOKAI) Nos. 4-132770(1992) and 9-100420(1997), since organic pigments are precipitated in the presence of an inorganic pigment to form a organic pigment layer on the surface of the inorganic pigment, the organic pigments fail to have a sufficient adhesion strength to the inorganic pigments as shown in the below-mentioned Comparative Examples. Further, since the obtained color agent has a high surface activity, the road marking material produced from such a color agent tends to undergo a large change in hue with the passage of time.
Also, in the method described in Japanese Patent Application Laid-Open (KOKAI) No. 7-331113(1995), organic pigments are charged together with inorganic pigments having a refractive index of not less than 2.2 and a coupling agent into a mixer, and stirred and mixed together therein to adhere the organic pigments onto the surface of the inorganic pigments. However, as shown in the below-mentioned Comparative Examples, the adhesion strength of the organic pigments onto the inorganic pigments tends to become insufficient as compared to the color agent for a road marking material according to the present invention in which organic pigments are adhered onto the surface of inorganic particles through a gluing agent coating layer. Therefore, a road marking material produced from the above conventional color agent may fail to show sufficient alkali resistance, abrasion resistance and aging resistance.
In addition, in Japanese Patent Application Laid-Open (KOKAI) Nos. 8-209030(1996) and 2001-220550, there are described heat-melting type road marking paints comprising caking resin, color agent and filler in which a pigment composition containing organic and inorganic pigments is used as the color agent. However, in these prior publications, the surface activity of the color agent is not taken into consideration. Therefore, it is suggested that the road marking material produced from such a color agent tends to undergo a large change in hue with the passage of time.
Meanwhile, in Japanese Patent Application Laid-Open (KOKAI) No. 2001-262297, there are described composite particles produced by adhering organic pigments onto the surface of white inorganic particles through a gluing agent. However, the object of this KOKAI is to suppress desorption of the organic pigments from the surface of the white inorganic particles, and this KOKAI is silent in the surface activity of the obtained composite particles.
As a result of the present inventors' earnest studies, it has been found that when composite particles having an average particle diameter of 0.01 to 10.0 μm which are produced by adhering 1 to 500 parts by weight of organic pigments onto 100 parts by weight of inorganic particles through a gluing agent and which may be further coated with a fatty acid, a fatty acid metal salt or a coupling agent, are used as a color agent for a road marking material, the obtained road marking material can show a less change in hue with the passage of time and an excellent retroreflective property. The present invention has been attained on the basis of the finding.